Remove ~feature_flag reviewer category from Danger

danger/roulette/Dangerfile

@@ -75,6 +75,8 @@ changes.delete(:none)
 changes.delete(:docs)
 # No special review for changelog needed and changelog was never a label.
 changes.delete(:changelog)
+# No special review for feature flags needed.
+changes.delete(:feature_flag)
 categories = changes.keys - [:unknown]
 
 # Ensure to spin for database reviewer/maintainer when ~database is applied (e.g. to review SQL queries)